Referring to FIG. 1, an exemplary network 100 including multiple nodes is shown. The exemplary network 100 may be, for example, a radio access network for high speed wireless data applications. Typical radio access networks, like that shown in FIG. 1 include one or more Access Terminals 102 (AT), Base Stations 104 (BTS), and Base Station Controllers 106 (BSC). A PDSN 108 interfaces between the IP network and the radio access network. The BSC 106 receives data from the core network 110 and passes the data to the BTS 104 so that the BTS can transmit the data to the AT 102 over the wireless link 120. Data is communicated through the reverse direction as well and passed from AT 102 to the core network 110. In general, each node consists of multiple functional components or units, where for example, each component is responsible for providing different functions or services. For example, at a Base Station, there may be a cell radio control unit, modem card unit and radio/amplifier unit to fulfill the overall function of a base station.
To further describe the information transmission between BSC and BTS, the protocol stacks 200 between the BSC and the BTS are shown in FIG. 2. As can be seen, there are multiple layers of protocols on each node to handle the peer-to-peer communications. As shown in FIG. 2, a Traffic Processor (TP) in the BSC receives packets from core networks via the Packet data service node (PDSN). The packets entering the BSC are IP packets encapsulated with GRE (Generic Routing Encapsulation) packets. The BSC processes the GRE packets and forms RLP (Radio Link Protocol) frames. RLP frames will be further passed to lower layers of RMI, UDP or TCP, and finally be formed into an IP packet that is sent over to the cell site.
Each layer of a protocol usually defines a Maximum Transmission Unit (MTU), which is the largest frame size that can be transmitted over the physical network. Messages longer than the MTU must be divided or fragmented into smaller frames. This operation is called fragmentation. The layer 3 protocol, which is IP in this example, extracts the MTU from the layer 2 protocol (e.g., Ethernet, etc.), fragments the messages into that frame size and makes them available to the lower layer for transmission.
In the illustrated radio access network scenario of FIGS. 1 and 2, the MTU size of the IP layer at the TP is 1500-bytes. The RLP frame size, however, is only 128-bytes. To improve the transport efficiency, i.e., to transport more data with the fixed protocol header, the RMI (Remote Method Innovation) protocol can aggregate or bundle the RLP frames together to form a large RMI message. The maximum bundling factor in this example is 11 so that the RMI message can be encapsulated in an IP packet fitting in the 1500-byte size after passing through the UDP or TCP layer.
A large bundling factor is generally preferred, since a large bundling factor increases the transport efficiency by sending more data with the same overhead. In practice, the bundling factor depends on the number of RLP frames currently in a buffer waiting for transmission. It is not always possible, however, to have enough RLP frames to generate a large IP packet sent to the cell. The bundling factor could be increased by intentionally delaying the bundling and transmission of the frames so that more arrival frames can be aggregated together. Blindly implementing such a scheme, however, will increase the packet delay and degrade performance.
Flow control mechanisms are often used to regulate the transmission rate so as to neither overflow nor underflow a receiver or a network. In one example of such flow control mechanisms, a window based flow control algorithm is in place to adjust the data transmission from BSC to BTS. The BTS informs the BSC via a flow control indication message of an advertisement window size, e.g., in number of frames. The BSC then determines its transmission window size and transmits frames within that transmission window. For example, assume the BTS advertises a window size of 50 frames after frame number 10. This means that the BSC can transmit frame number 11, 12, up to frame number 60. If the last frame the BSC has transmitted is frame number 15, the transmission window size at the BSC will be updated as 45, which means 45 frames after frame number 15 can be transmitted. As will be explained this flow control indication message could tell additional information about the congestion status at the BTS that can be utilized by the BSC in the aggregation process. Accordingly, there is a need for an aggregation methodology that makes use of flow control information.